Kaposi's sarcoma-associated herpesvirus (KSHV) in bone marrow biopsy from patients with multiple myeloma: PCR amplification of orf26 but not orf72 and orf75 sequences

Molecular biology of KSHV lytic reactivation

Kaposi’s sarcoma-associated herpesvirus (KSHV) primarily persists as a latent episome in infected cells. During latent infection, only a limited number of viral genes are expressed that help to maintain the viral episome and prevent lytic reactivation. The latent KSHV genome persists as a highly ordered chromatin structure with bivalent chromatin marks at the promoter-regulatory region of the major immediate-early gene promoter. Various stimuli can induce chromatin modifications to an active euchromatic epigenetic mark, leading to the expression of genes required for the transition from the latent to the lytic phase of KSHV life cycle. Enhanced replication and transcription activator (RTA) gene expression triggers a cascade of events, resulting in the modulation of various cellular pathways to support viral DNA synthesis. RTA also binds to the origin of lytic DNA replication to recruit viral, as well as cellular, proteins for the initiation of the lytic DNA replication of KSHV. In this review we will discuss some of the pivotal genetic and epigenetic factors that control KSHV reactivation from the transcriptionally restricted latent program.

Reflections on the interpretation of heterogeneity and strain differences based on very limited PCR sequence data from Kaposi's sarcoma-associated herpesvirus genomes

Ever since the original identification of fragments of KSHV DNA in Kaposi's sarcoma (KS) tissue by Chang et al. in 1994, PCR has been used successfully and extensively to detect the virus in clinical samples from the accepted etiological diseases of KS, PEL and MCD. However, a number of other clinical and epidemiological studies claiming evidence for KSHV in multiple myeloma or sarcoid and more recently in primary pulmonary hypertension, as well as claims about the biological significance of DNA sequence polymorphisms based just on small ORF26 PCR DNA fragments have not been convincing. Here, we evaluate the validity and interpretations of previous results in the context of both the observed rates and global patterns of sequence variability within an extended ORF26 locus, as well as from the perspective of the overall levels of KSHV variability found after sampling multiple loci across the complete KSHV genome. The results cast doubts on most claims for biological significance for these polymorphisms, which instead correlate with viral subtype clustering arising from geographic and ethnic divergence of the ancestral human hosts. In addition, we describe several observations that help to explain likely sources of the often either unexpectedly high or unexpectedly low levels of sporadic variability seen in the PCR DNA sequence data reported in some of those studies.

INFECTION WITH HUMAN HERPESVIRUS 8 AND TRANSPLANT-ASSOCIATED GAMMOPATHY

BACKGROUND

The role of human herpesvirus (HHV)-8 in the pathogenesis of multiple myeloma and its pre-malignant state of monoclonal gammopathy is unclear. HHV-8 is transmitted by organ transplantation, representing a unique model with which to investigate primary HHV-8 infection.

METHODS

The authors studied the incidence of clonal gammopathy in renal transplant recipients and correlated it with previous and recent HHV-8 infection.

RESULTS

Clonal gammopathy was observed in 31 of 162 (19%) HHV-8-seronegative patients, in 5 of 17 (29%) HHV-8-seropositive patients, and in 9 of 24 (38%) HHV-8 seroconverters within 5 years after transplantation. Gammopathy was often transient, and no progression to myeloma was observed. Two patients with persistent gammopathy developed B-cell lymphoma. In a logistic regression model, HHV-8 serostatus of the graft recipient was significantly associated with subsequent development of gammopathy, with a relative risk (RR) of 1.9 and a 95% confidence interval (CI) of 0.5 to 6.4 for an HHV-8-seropositive recipient and an RR of 2.9 and a 95% CI of 1.01 to 8.0 for seroconverters as compared with baseline (HHV-8 seronegative). Other significant variables were cytomegalovirus (CMV) serostatus and the intensity of immunosuppression (RR of 10.4 and 95% CI of 2.6-41.7 for a CMV-negative recipient with a CMV-positive donor vs. a CMV-negative recipient with a CMV-negative donor and RR of 17.6 and 95% CI of 2.0-150.8 if OKT3 was used vs. no use of antilymphocytic substances).

CONCLUSIONS

Transplant recipients with HHV-8 infection are more likely to develop clonal gammopathy. However, this risk is much lower than the risk conferred by CMV infection and antilymphocytic therapy, arguing against a major role of HHV-8 infection in the pathogenesis of clonal plasma cell proliferation.

Detection and characterization of human herpesvirus-8-infected cells in bone marrow biopsies of human immunodeficiency virus-positive patients

We studied 15 bone marrow biopsy specimens from patients with human immunodeficiency virus infection for detection of Kaposi sarcoma herpesvirus (KSHV/HHV-8) DNA sequences by a very sensitive and specific polymerase chain reaction (PCR) assay (with 3 different sets of primers). In addition, we used immunohistochemistry with antiviral interleukin-6 (vIL-6) and anti-latent nuclear antigen-1 (LNA-1) antibodies to localize the infected cells on tissue sections. Among the 15 samples, 6 had positive PCR results with the 3 sets of primers (orf26, orf72, orf75). Interestingly, in 2 of these 6 patients (both with Kaposi sarcoma) vIL-6 and LNA-1 were detected in mononuclear lymphoid cells but not in stromal cells of the bone marrow. The detection of vIL-6--positive lymphoid cells in bone marrow suggests a homing for HHV-8--infected elements in this tissue. The local release of vIL-6 may play some role in the plasmacytosis observed in bone marrow in the acquired immunodeficiency syndrome. HUM PATHOL 32:288-291.

Recent advances in multiple myeloma

Multiple myeloma is the second most common hematologic malignancy, with approximately 15,000 new cases each year in the United States. Our understanding of the pathophysiology underlying myeloma continues to expand, but the cause of this plasma cell dyscrasia remains unclear. Though controversy remains regarding a possible viral cause of myeloma, evidence suggesting a role for the human herpesvirus-8 is mounting. The roles of cytogenetic abnormalities as well as aberrant angiogenesis and cytokine expression in the etiology of myeloma continue to be explored and may lead to future therapeutic strategies. Transplantation in myeloma is rarely curative but offers clinical benefit not only for young but possibly for older myeloma patients as well. Newer bisphosphonates may offer greater ease of administration, improved efficacy, and possibly even enhanced antitumor effect. Finally, thalidomide offers significant clinical benefit to patients with myeloma previously refractory to multiple agents, and its role in early stages of the disease is under investigation.